This invention relates to burglar alarm servicing equipment, and more particularly to an apparatus for aiding in the detection of circuit faults in a burglar alarm system.
A typical burglar alarm system includes a closed loop circuit path that extends throughout a premises being protected. The circuit loop would generally include burglar alarm tapes along windows and doors, burglar alarm switches at various locations, and might also include vibration detectors and other type of sensors to detect unauthorized entry. All of these sensors and tapes are then interconnected into a complete closed loop path. An alarm is placed within the path and the ends of the path are connected to the alarm circuit terminals which derive power from either house current or battery power during emergency times. When an unauthorized entry occurs, a break in the tape will open the circuit, or one of the sensors will open, to open the circuit. Such opening of the circuit causes the alarm to sound.
After installation, as a result of environmental conditions, deterioration and the like, parts of the circuit may accidentally break and false alarms occur. When a full break occurs, typically a service repairman will use a continuity tester to find the breakage in the circuit in order to repair it. By measuring the resistance across various points in the circuit with an ohmmeter and the like, it is possible to detect which part of the circuit has the infinite resistance, thereby representing an open circuit giving an indication of a breakage.
More frequently, however, short intermittent breaks called "swingers" may occur. Such "swingers" may not occur for months at a time and may last only a second or so when they do. They may show up only when wind rattles a window, opening a hairline crack in a foil loop, or when wood swells or shrinks, causing electrical contacts to part. Frayed wires or loose connections can momentarily separate due to vibration or temperature changes, then "heal" themselves later, giving no clue to the trouble. A thin film of dirt or corrosion could also be the reason for intermittent contact failure. The alarm may accidentally go off and then stop by itself. The loose connection, or partial break, will cause sounding of the alarm when armed or intermittent circuit reading on a meter or LED circuit indicator.
Servicemen find it difficult to locate such swingers because of their intermittent action. In order to detect such swingers, the service repairman will typically connect an ohmmeter or other type of resistance measuring device across the two entry points into the circuit line at their connection to the alarm circuit loop terminals. When connecting an ohmmeter to the alarm circuit loop, the circuit wires are removed from the alarm circuit loop terminals. Resistance is measured across the alarm circuit loop only. The repairman must then proceed around the entire premises manually shaking or moving each of the switches, wires, detectors, and sensors. As each one is manually moved or adjusted, the serviceman must return to the ohmmeter and see if there occurred an increase or decrease in the reading of the meter. Typically, the resistance should drop. However, occasionally it may increase, especially if there are more than one such swingers in the line. Many times, however, the resistance reading in a circuit containing an intermittent break, will read satisfactorily across the two entry points. Many swingers swing too fast to be detected using the methods used today.
However, for detecting each sensor that is moved or adjusted, he must again go back to the ohmmeter. For this reason, typically, two people are necessary in order to test a burglar alarm system having swingers present in the circuit. One person proceeds throughout the premises testing the wires and switches while the other monitors the readout at the ohmmeter.
Because of the difficulty detecting such swingers requiring inconvenience for one person to test and thereby necessitating the presence of two individuals, there is need for an improvement in the apparatus and methods utilized for detecting such burglar alarm faults.